This invention relates, generally, to a heat exchanger and, more particularly, to a heat exchanger for use with a film developing apparatus.
Film developing apparatuses, such as those used to develop x-ray film, typically consist of a plurality of driven rollers for conveying an exposed film through a liquid developer bath, a liquid fixer bath, and a rinsing bath. The developer and fixer baths typically consist of alkaline and acidic solutions, respectively, and the rinsing bath typically consists of water.
As is well known, the developer and fixer solutions must be heated and maintained within a narrow temperature range to properly develop the film. In the past this was done by locating a heating coil in the developer and fixer baths. The heating coil would be energized in response to a signal generated by a temperature sensor disposed in the baths. The coils located directly in the baths are satisfactory if the containers holding the baths are constructed of stainless steel. However, in recent years, the stainless steel baths have been replaced by plastic containers because of their lower cost and greater ease of manufacturing. The known heating elements, when placed directly in the plastic containers can melt the plastic and, in extreme conditions, cause the containers to catch on fire. Attempts to carefully monitor the heating elements to avoid these undesirable results have proved unsuccessful.
Thus a heat exchanger that can heat the developer and fixer solutions without contacting or being in proximity to the plastic containers or other plastic components is desired. Such a heat exchanger, while having particular applicability to the film developing art, can be used in any application where the transfer of heat to a fluid is desired.